1. Field of the Invention
The present invention relates to a power unit having an engine and a continuously variable transmission (CVT), and to a vehicle incorporating same. More particularly, the present invention relates to a power unit having a hydraulically-operated CVT and to an arrangement (layout) of various components of the CVT within the power unit.
2. Description of the Backgound Art
There are known power units for a vehicle, such as a motorcycle, having an engine and a CVT. In such power units, a power transmission chamber, which is integrally formed with a crank chamber of the engine, is generally disposed behind the crank chamber of the engine.
The continuously variable transmission, such as a wet belt-type automatic transmission, is arranged in a lowermost portion of a common chamber formed by the crank chamber and the power transmission chamber. The common chamber functions as the crank chamber as well as the power transmission chamber.
In the power unit having the continuously variable automatic transmission (automatic transmission), an oil pan is arranged in a lower portion of the power unit. The oil pan receives oil for lubricating the engine and various components of a power transmission system.
The power unit includes a drive pulley and a driven pulley, which are connected to the engine (e.g., to a crankshaft of the engine), arranged in the power transmission chamber.
Further, the drive pulley and the driven pulley are arranged in a vertically displaced manner such that rotational axes of the drive pulley and the driven pulley are arranged in parallel to an axis of the crankshaft of the engine. In such configurations, both drive and driven pulleys overlap each other when viewed from above, in a top plan view.
An example of such known power unit is disclosed in the Japanese Patent Document JP-A-63-103784. According to the Japanese Patent Document JP-A-63-103784 (page 1, FIG. 2), the power unit includes a starter clutch which is mounted on a shaft portion of a drive pulley shaft. The starter clutch transmits a rotational drive force of the engine to a drive wheel at the time of starting a vehicle and interrupts the transmission of the rotational drive force of the engine to the drive wheel at the time of stopping the vehicle.
Here, since in the power unit of the vehicle according to the Japanese Patent Document JP-A-63-103784, the starter clutch is mounted on the shaft portion of the drive pulley shaft, the starter clutch is disengaged from a gear arrangement before the CVT assumes a low speed state at the time of stopping the vehicle. However, there exists a possibility that the CVT is driven in a high speed state at the time of starting the vehicle next time thus lowering the maneuverability of the vehicle.
Further, a large-sized starter is required for starting the engine when the starter clutch is mounted on the shaft portion of the drive pulley shaft because a large load is applied to the starter since the starter drives the CVT while rotating the crankshaft. Therefore, mounting of the starter clutch on the shaft portion of the drive pulley shaft leads to a requirement of a large-sized, high capacity starter.
The present invention has been made to overcome such drawbacks. Accordingly, it is an object of the present invention to provide a power unit for a vehicle which enhances the maneuverability at the time of starting the vehicle by bringing a CVT into a low speed state at the time of stopping the vehicle. It is also an object of the present invention to provide a power unit which reduces a load applied to the starter by interrupting the transmission of a rotational drive force of the crankshaft to the drive pulley at the time of starting the engine.